A hammertoe is simply a contracted or bent toe. In the early stages, it can be stretched (extended) or flexed (contracted). Over enough time, the toe or toes can become stiff, and even manually trying to straighten them out can become difficult and painful. An end stage hammertoe can fuse into a deformed position from arthritis.
Treatments include accommodative shoes, pads, and surgery to straighten the toe when the condition becomes unmanageable.